Don McGough lost his job as a union steelworker. He found a new position and a decade later, he voted no when the machinists’ union tried to organize workers at his company, JWF Industries, in Pennsylvania. “There are so many companies that just closed their doors because the union wouldn’t budge,” he says.

While unions representing U.S. manufacturing might — auto and steel — have become smaller, the emphasis in recruiting new members has shifted to the service sector.

The Service Employees International Union, which represents nurses and lower-wage service employees including janitors, security, hospital, home health and child care workers, has doubled in size since 1996, to 2.1 million workers. It says it has added 50,000 workers annually in the last decade.